1. Field
Embodiments disclosed herein relate to a method and system for performing a flow check with a closed-to-atmosphere drilling system, resulting in improved accuracy compared to current open-to-atmosphere methods. Using methods disclosed herein, the presence of a self-sustained influx of formation fluids into a wellbore may be quickly and safely confirmed or ruled out.
2. Background
Well control techniques are used in oil and gas operations such as drilling, well workovers, and well completions to maintain fluid pressure at certain points in a wellbore above a formation pressure and prevent influx of formation fluids into the wellbore—known as “overbalanced” differential pressure. With the pumps on and fluid circulating, a combination of hydrostatic pressure, friction pressure and surface pressure may combine to maintain an overbalanced differential pressure in a wellbore. In the event that an “underbalanced” differential pressure comes to exist in the wellbore—where fluid pressure at certain points in the wellbore is less than the formation pressure—formation fluids may flow into the wellbore. The fluid influx will continue until either the fluid pressure in the wellbore is increased, or the formation pressure decreases. This type of fluid influx may be referred to as a “self-sustained” influx. The self-sustained influx should be stopped and the unwanted fluid safely removed from the wellbore before continuing with oil and gas operations. Notably, a self-sustained influx is often generally characterized in the industry as a “kick” along with other non-self-sustained influxes requiring different or no remedial action. As explained below, this exacerbates problems with accurately identifying a self-sustained influx with current open-to-atmosphere annulus fluid systems.
A flow check procedure is a method by which a driller may, upon suspicion or sign of a self-sustained influx, attempt to confirm whether such an event is indeed occurring before initiating well control techniques. A typical flow check procedure involves positioning the drill bit at a suitable position above the bottom of the wellbore/borehole, stopping rotation of the drillstring, and then stopping the mud pumps. The driller then checks to see if there is any flow returning from the well annulus (i.e., whether the well is “flowing”) with the pumps off. If the well is flowing with the pumps off, the driller may conclude that some type of influx is entering the wellbore.
Conventional flow check procedures today are performed entirely with the BOP open, i.e., with an open-to-atmosphere annulus fluid system. Very often, using an open-to-atmosphere system is inadequate for the rig crew to accurately and quickly come to a conclusion as to whether a self-sustained influx is indeed happening or not due to a variety of other benign causes for such a perceived influx. For example, on floating rigs, relatively small yet significant self-sustained influxes may be difficult to observe because the conventional flow check procedure may be affected by rig motion and heave effects. Additionally, in some situations there may be outflow from the well that continues after the mud pumps are turned off due to thermal effects, well decompression, or flow back from fractures filled previously in (i.e., generally known as “ballooning”). Even though these conditions may cause outflow from the well, in such cases the flow is generally not due to a self-sustained influx of formation fluids into the wellbore. Therefore, they do not constitute kicks that might otherwise require precise control or response using well control procedures.
Moreover, flow check procedures take time that is often prescribed by procedure (e.g., requiring a minimum of 10, 15, or 30 minutes). Drillers may hesitate to risk stopping drilling operations for such periods until/unless clear justification exists. And worse yet, a driller who has had the experience of stopping to perform a flow check procedure only to find no self-sustained influx existed may be less likely to quickly do so again—even if new circumstances justify it—if the earlier flow check resulted in delay, costs or operational problems that could otherwise have been avoided by not performing the flow check.
Currently, the industry is ill-informed, prior to shutting in a well, to properly and accurately detect and distinguish between self-sustained influxes requiring well control techniques and temporary influxes that do not. Instead, the industry prefers to deal with all potential influxes in a “one size fits all” manner. This leads to a multitude of costly and inefficient false alarms and misleading information.
3. Identification of the Objects of the Invention
A primary object of the invention is to provide a method of quickly and accurately identifying a self-sustained influx of fluids into a wellbore, such as prior to initiating well control techniques.
It is another object of the invention to provide a method of accurately ruling out the presence of a self-sustained influx of fluids into said wellbore.
Another object of the invention is to provide a system for identifying a self-sustained influx of fluids into a wellbore.